1. Field of the Invention
The present invention relates to the field of structural engineering and, more particularly, reinforced concrete based structures, such as columns and walls, and wrapping methods and mechanisms for strengthening such structures. More specifically, the invention pertains to a wrapped structure and wrapping process for improving the structure's axial, flexural, and shear strength, as well as its ductility and stiffness.
2. Description of the Related Art
Conventional techniques for wrapping columns or walls involve winding fabric made of filament or fiber around at least a portion of the structure. The fiber fabric typically is made of glass fiber, carbon fiber, or aramids fiber. The amount of fiber wrapping applied to a column or wall depends upon the type and degree of strengthening that the specific structure requires.
Thin filament or fiber fabric wrapping, referred to hereinafter as fiber reinforced plastic (FRP) wrapping, is known in the art and described generally in U.S. Pat. No. 5,218,810, which is hereby incorporated by reference. When a circular column has FRP wrapping wound around it, the wrapping exerts a substantially uniform confining pressure around the entire circumference of the column because of the circumferential membrane (axial) stiffness of the wrapping system. As a result, the FRP confines the entire cross-section of the wrapped structure.
Conventional methodologies of applying FRP wrapping have been successful in improving the strength and ductility of circular columns. Considerations applicable to noncircular columns and walls, however, are different. This is because the axial stiffness of the filament or fiber winding in the transverse direction of the column or wall (i.e., in a direction perpendicular to the axis of the column or wall) cannot provide any significant confinement along the flat sides or planar surfaces of the noncircular structure. As such, most of the confining pressure falls on the corners of the column or wall. Thin FRP wrapping possesses negligible transverse flexural stiffness and, therefore, considerable portions of the noncircular cross-section remain unconfined. Significantly, most columns or walls are noncircular. Accordingly, there is a need for a wrapping system that is adaptable to all types of columns or walls.